An important message in the "Let's Take Care of Our Summer Air" summer ozone campaign is "Stop At the Click." But a question asked by citizens numerous times over the years is "Why not?!" This answer published recently in the Rocky Mountain News explains some of the reasons why, or more accurately...why not.
Ask!: To top it all off can be hazardous
Hank wanted to know why we're advised against topping off our gas tanks, especially in the summer. That advice, of course, presumes that we know what topping off means.
Generally speaking, topping off refers to filling a container to the top; in the case of gas tanks, Perry wrote, it means adding fuel after the nozzle has automatically shut off.
Perry and Elmo, another writer, said a danger of topping off is that summer sun and heat can cause gas to expand. If a tank has been filled to the top, expanding gas can leak from the tank, causing a fire hazard and air pollution from evaporating gas. Fred and Perry wrote that topping off the tank could cause problems with the evaporative emissions system, which Fred says has been on cars since 1980.
The Environmental Protection Agency (epa.gov/donttopoff) says that in areas with ozone issues like ours, gas-station pumps are equipped with vapor- recovery systems that return gas fumes to the storage tanks so they don't escape into the air. "Topped-off" gas could be drawn into this system and returned to storage, meaning you'd pay for gas you didn't get. And the additional gas could disable the station's vapor-recovery system, contributing further to pollution and maybe knocking out the pump, according to the EPA.
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